Ultrahard materials, such as PCD and CBN, are useful in a variety of industrial applications, such as the drilling of rock formations. For example, PCD is commonly used in earth-boring drill bits in both petroleum extraction and mining operations. Ultrahard materials are particularly useful in such applications because they are extremely abrasion-resistant, and can withstand high temperatures and frequent impact with other hard materials, such as rock formations.
PCD is typically formed by subjecting diamond crystals to a high temperature high pressure (HTHP) sintering process in the presence of a catalyst material, such as a Group VIII metal or an alloy thereof. Cobalt, nickel and their alloys are particularly useful as catalysts during PCD formation. Similar catalyst-based processes may be used to form other ultrahard materials.
It can be beneficial to remove the catalyst from the PCD or other ultrahard material after the PCD is formed. Otherwise, differences in thermal conductance and thermal expansion between the catalyst and the ultrahard material can accelerate wear of the ultrahard material during use.
Various methods exist for removing catalyst from ultrahard materials, including so-called acid leaching and electrolytic processes.